The present invention relates to an imaging apparatus and a subject moving device thereof, and particularly to an imaging apparatus for imaging an image of a subject moved to an imaging space, and a subject moving device thereof.
In an imaging apparatus such as an X-ray CT (Computed Tomography) apparatus or the like, a subject moving device moves a subject to an imaging space, and a scanning gantry scans the subject moved to the imaging space to obtain row data of the subject. An image about a tomographic plane of the subject is generated by reconstruction on the basis of the obtained row data. Such an X-ray CT apparatus has been utilized for a wide range of uses such as a medical use, an industrial use, etc.
The scanning gantry in the X-ray CT apparatus includes an X-ray tube and an X-ray detector. The X-ray tube applies X rays to the subject and the X-ray detector detects the X rays transmitted through the subject to generate projection data of the subject. Here, the scanning gantry rotates the X-ray tube and the X-ray detector with a body axial direction of the subject as an axis. The scanning gantry applies the X rays from the periphery of the subject and acquires projection data corresponding to a plurality of view directions as row data of an image.
In the X-ray CT apparatus, the subject moving device includes a table section and a table moving section. The table section supports the subject and the table moving section moves the table section into an imaging space of a scanning gantry (refer to, for example, a patent document 1).
[Patent Document 1] Japanese Unexamined Patent Publication No. 2004-173756
There is a case in which an actuator is used in the above table moving section to move the table section. The actuator is of, for example, a hydraulic actuator. The actuator holds oil-like fluid inside a cylinder and expands and contracts over its entire length according to the pressure of the fluid held thereinside to move the table section. The actuator adjusts a flow rate of the fluid held in the cylinder using, for example, a plunger type proportional controlled valve to thereby control pressure based on the fluid held thereinside. Thus, the actuator expands and contracts and hence changes in its entire length, thereby moving the table section. Using the actuator in the table moving section makes it possible to move the table section quietly and smoothly and realize miniaturization, durability, reliability, a cost reduction and the like of the apparatus.
However, there was a case in which when the table section was moved downward as viewed in a vertical direction, it became difficult to move the table section smoothly. There were, for example, cases in which when the table section was moved downward up to a reference position as viewed in the vertical direction, the table section was moved to a position placed further downward beyond the reference position and a shock was given to the subject due to a descending operation. This principally results from the fact that since the pressure based on the fluid held in the cylinder of the actuator differs according to the position of the table section at the start of the movement thereof downward, the flow rate of the fluid adjusted by the proportional controlled valve is different from a reference value. In addition to the case referred to above, there was a case in which since the pressure based on the fluid lying inside the cylinder differed according to the weight of a subject to be imaged or photographed, it became difficult to move the table section smoothly in like manner. There was also a case in which since the pressure based on the fluid lying inside the cylinder differed due to changes with time and variations in the apparatus, it became difficult to move the table section smoothly in like manner.
Therefore, the above imaging apparatus encountered difficulties in handling it with ease and caused a reduction in its operability.